1. Field of the Invention
The present invention relates to a toner to be used in an image-forming method such as an electrophotographic method, an electrostatic recording method, an electrostatic printing method, or a toner jet method.
2. Description of the Related Art
High reliability and consideration for the environment have been strongly requested of a printer or copying machine in recent years.
The term “high reliability” means not only that the printer or copying machine can continue to output images at levels comparable to that of an initial image even when images are printed with the printer or copying machine over a long time period but also that the printer or copying machine is user-friendly. To be specific, the printer or copying machine is requested to maintain good developing performance, good transferring performance, and good winding resistance irrespective of the environment under which the printer or copying machine is used and irrespective of what kind of a transfer material is used. In addition, the term “consideration for the environment” means that the printer or copying machine is requested to be capable of being driven with a low power consumption so as to respond to energy savings. To be specific, the printer or copying machine is requested to have good low-temperature fixability.
A color toner obtained by subjecting a polymerizable mixture containing styrene and α-methylene aliphatic monocarboxylates for producing polar and non-polar polymers to suspension polymerization has been proposed with a view to improving transparency in an OHP sheet. The proposal discloses a color toner having the characteristics (see Patent Document 1) that the toner contains a mixture of a polar polymer and a non-polar polymer as a binder resin, the polar polymer is unevenly distributed on the surfaces of the particles of the toner, and the toner has a Wardell sphericity of 0.95 to 1.00 and a melt viscosity at 130° C. of 10 to 33,000 poises.
A proposal has been made with a view to obtaining a toner having the characteristics that the toner is excellent in blocking resistance even under a high-temperature, high-humidity environment, allows images to be fixed at low temperatures, is excellent in releasing performance, stably shows high developing performance, provides an image having a high image density, and shows a suppressed change in its performance even when the toner is used over a long time period. The proposal describes toner particles each containing at least two kinds of components including a high-softening-point resin (A) and a low-softening-point substance (B) and each having a structure separated into an A phase mainly formed of the high-softening-point resin (A) and a B phase mainly formed of the low-softening-point substance (B) (see Patent Document 2).
A toner for image formation having the following characteristic has also been proposed with a view to securing pulverizing performance, heat-resistant storage stability, offset resistance, transferring performance, low-temperature fixability, and flaw resistance (see Patent Document 3): at least one exothermic peak is present around the glass transition point of the binder resin of the toner in the second temperature increase process of the DSC curve of the toner.
Further, a toner having the following characteristics has been proposed with a view to securing gloss, color reproducibility, and the uniform stability of image gloss (see Patent Document 4): the binder resin of the toner has a weight-average molecular weight of 8,000 to 50,000 and a glass transition point of 40 to 55° C., and a thermoplastic resin having a weight-average molecular weight twice or more as high as that of the binder resin and a glass transition point higher than that of the binder resin by 5° C. or more is present near the surface of the toner.    Patent Document 1: JP 07-34126 B    Patent Document 2: JP 03184626 B    Patent Document 3: JP 2004-184561 A    Patent Document 4: JP 2006-053353 A